>>Using forward biased diodes as voltage references is shoddy
>>design. It isn't just cheap, it's skanky.
>It's not just cheap, it's /very/ cheap. You can get a dozen red leds
>for the cost of your inexpensive precision reference, and if you're
>building the thing and sourcing the parts then it's a completely valid
>design. When you make a million of them, the 19 cents per LED you save
>ends up being nearly $200,000. You can get red leds from hundreds of
>suppliers, and lead time is zero.
>
>So from a design perspective I can see it isn't ideal, but from a
>manufacturing, profit perspective it is /much/ better than a voltage
>reference. Remember that this is a value added troubleshooting feature,
>and (IIRC when I built mine) it only gave the chip the ability to
>monitor the voltages used - it isn't part of any feedback loop. And it
>gives you a power on indicator that you might've added anyway, so you
>are killing a few birds with a 1 cent part.

One other thing to add fuel to the fire: most *red* LEDs have a pretty
darn reasonable tempco - better than some cheap zener diodes!

Sorry to disagree with Dave but an experienced designer working with a
parts purchaser who understands and obeys a 'Do Not Substitute' label can
effectively use LEDs as voltage references. But I agree on one thing: its
not a good hobby technique just because of the variety of LEDs available.

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Subject (change)
ICD Schottkey diode